Japanese Spallation Neutron Source Research Articles

Development of microbubble generator for suppression of pressure waves in mercury target of spallation source

A MW-class mercury target for the spallation neutron source is subjected to the pressure waves and cavitation erosion induced by high-intense pulsed-proton beam bombardment. Helium-gas microbubbles injection into mercury is one of the effective techniques to suppress the pressure waves. The microbubble injection technique was developed. The selection test of bubble generators indicated that the bubble generator utilizing swirl flow of liquid (swirl-type bubble-generator) will be suitable from the viewpoint of the produced bubble size. However, when single swirl-type bubble-generator was used in flowing mercury, swirl flow of mercury remains at downstream of the generator. The remaining swirl flow causes the coalescence of bubbles which results in ineffective suppression of pressure waves. To solve this concern, a multi-swirl type bubble-generator, which consists of several single swirl-type bubble-generators arraying in the plane perpendicular to mercury flow direction, was invented. The multi-swirl type bubble-generator was tested in mercury and the geometry was optimized to generate small bubble with low flow resistance based on the test results. It is estimated to generate the microbubbles of 65 μm in radius under the operational condition of the Japanese Spallation Neutron Source mercury target, which is the sufficient size to suppress the pressure waves.

Pulse characteristics of epithermal neutrons from a spallation source

This paper discusses the feasibility of the use of epithermal neutrons from hydrogen moderators installed at a MW-class spallation neutron source. Pulse characteristics of epithermal neutrons at Japanese Spallation Neutron Source (JSNS) are studied by comparing with a reference light water moderator, which does not exist but is optimized at the JSNS target-moderator-reflector geometry. The performance in figure of merit expected from the JSNS hydrogen moderators at an epithermal neutron region are found to be 50–100%, depending on the neutron energy, compared to the reference light water moderator. JSNS could also be useful as an epithermal neutron source, although it was mainly designed as a cold and thermal neutron sources for the condensed matter research.

Numerical study on pressure wave propagation in a mercury loop

On-beam tests were carried out at the Los Alamos Neutron Science Center–Weapons Neutron Research (LANSCE–WNR) facility in June 2005 to investigate pressure wave mitigation in mercury targets for the MW-class spallation neutron sources under international collaboration between US Spallation Neutron Source (SNS) and Japanese Spallation Neutron Source (JSNS). A mercury loop was used for the target, a so-called In-Beam Bubbling Test Loop (IBBTL). The loop consists of the rectangular pipe of 25 mm × 50 mm 2 in cross section, 1.5 mm in wall thickness and 2 m in total length approximately. The SNS team set 8 strain sensors on the pipe wall to measure the strain propagation caused by the pressure wave. The maximum strain appeared at 350 mm apart from the proton-bombarded point at 5.5 ms after the proton bombardment. It is known that the propagation velocity of the pressure wave in mercury is ca. 1500 m/s and that of the stress wave in stainless steel is ca. 5000 m/s. However, the apparent wave propagation velocity in the IBBTL was lower than those velocities and was observed to be 65 m/s. Numerical analysis was carried out to understand the strain propagation in the pipe wall of the IBBTL. Numerical results showed that the maximum strain at 350 mm apart from the beam spot appeared at 5.5 ms after proton bombardment in good agreement with experimental results.

Experimental study of cosmonuclear physics at J-PARC

JSNS, the Japanese Spallation Neutron Source, is a forthcoming 1MW spallation neutron source. Since it is highly intense and has low background, it will provide a unique opportunity to study neutron-induced nuclear reactions relevant to astrophysics with excellent sensitivity and accuracy. Details of the JSNS facility and a plan for an experimental study of cosmonuclear physics are presented.

DPA calculation for Japanese spallation neutron source

A neutron generating target and surrounding components, such as moderators and proton-beam windows, of intense pulsed spallation sources suffer serious radiation damage. In order to construct a maintenance scenario of the Japanese Spallation Neutron Source, the life estimation of those components due to the radiation damage becomes indispensable. For this purpose, we calculated DPA values of the important components, based on the calculation of displacement cross-sections using PHITS and NJOY codes with the LA150 library. Maximum DPA values at the end of 5000 MW h are 3.9 for the target vessel, 2.8 for the reflector and moderator vessels, and 0.4 for the proton-beam window. We also discuss the effect of the proton-beam profile and proton-energy dependence on the DPA values. Briefly, we showed the calculation result on the helium and hydrogen production.

Development of Drabkin energy filters for JSNS project

We have a plan to install Drabkin energy filters for neutron spectrometers at the Japanese Spallation Neutron Source (JSNS) project. Combined with a high-intensity coupled moderator, a Drabkin energy filter could be very useful to obtain a high-resolution polarized beam with higher intensity than a beam from a decoupled moderator. Hence, it could bring about a breakthrough for more efficient use of neutrons at neutron spectrometers. We have developed a Drabkin energy filter which has 10 periods of spatially oscillating magnetic field and measured spin–flip probabilities as functions of field strength and of neutron wavelength. In this paper, results of the performance tests of Drabkin energy filters are presented and discussed.

Japanese spallation neutron source

The Japanese ‘Joint Project’ is a new project to pursue frontiers in particle physics, nuclear physics, materials science, life science and nuclear technology, using a new proton-accelerator complex with the highest beam power in the world. This project had been jointly proposed by the High Energy Accelerator Research Organization (KEK) and the Japan Atomic Energy Research Institution (JAERI), and was approved at the end of 2000. This accelerator complex allows the production of a variety of intense secondary-particle beams such as neutrino, neutron and muon beams. As one of the major facilities in this project, the next generation of a pulsed spallation neutron source with a power of 1 MW will be constructed by the end of 2006, which is comparable to the new pulsed sources realized in the USA and Europe. It can open exciting prospects for materials and life sciences. In this paper, design activities for the new neutron-science facility are summarized.

Summary of the Fourth International Workshop on Spallation Materials Technology (IWSMT-4)

The Fourth International Workshop on Spallation Materials Technology (IWSMT-4) took place on 8–13 October in Schruns, Austria. The present volume contains the proceedings of this workshop. 53 scientists from Europe, USA and Japan presented 44 papers covering a wide range of topics including the status of spallation target R&D activities, effects of radiation damage, hydrogen, helium and other transmutation impurities in materials, particle transport calculations, heavy liquid metal corrosion and compatibility, and materials engineering. The main progress, with an emphasis on materials technology in different projects, namely the US Spallation Neutron Source (SNS), the European Spallation Source (ESS), the Japanese Spallation Neutron Source (JSNS), the Swiss Spallation Neutron Source (SINQ) and the US Accelerator Production of Tritium facility (APT) was overviewed. Progress from the European TECLA and SPIRE programs was described. The achievements of investigations in the last two years on mechanical properties and microstructures of materials under high-energy proton (spallation), neutron and low energy ion irradiations were reported. The latest results from studies on corrosion and embrittlement effects of heavy liquid metals (Hg, Pb–Bi and Pb) were presented. Some critical issues of liquid metal technology related to accelerator driven systems (ADS), e.g. oxygen control and oxygen measurements were discussed.